Suggest be case insensitve

Scenario: I want to use Xnest. I type 'xnest', and the shell just tells me command not found and no suggestion. Oops, doesn't Ubuntu ship Xnest? Later I know I must type 'Xnest' to know which package I should install.

I looked at the code:

    def lookup(self, key):
        if self.db and self.db.has_key(key):
            return self.db[key]

We are using exact matching.

I suggest ignore letter cases when looking up in the databases, since we usually do not know or remember the exact cases of commands.